Lithium and boron isotopic compositions of olivine in chondrules from carbonaceous and ordinary chondrite meteorites: Implications for the origin of solar 11B/10B ratio

The origin of solar B-11/B-10 ratio(-4) remains an open question. It has been thought that a significant por-tion of boron in the Solar System was derived from continuous spallation nucleosynthesis during inter-actions between Galactic Cosmic Rays and C-N-O nuclei in the interstellar medium. However, because GCR-produced boron is characterized by B-11/B-10 similar to 2.5, an endmember with B-11/B-10 > 4 is required to account for the solar B-11/B-10 ratio. Two leading hypotheses for the sources of B-11-rich components include low energy spallation in the Sun's parental molecular cloud and the neutrino process during the super-nova explosions. In this study, lithium and boron elemental and isotopic compositions of seven por-phyritic olivine chondrules and one isolated olivine crystal from four meteorites (Allende, Yamato 81020, Asuka 12236, and QUE 97008) were determined in-situ to help constrain which of the two nucle-osynthetic mechanisms has most likely supplied the forming Solar System with extra B-11. Apparent iso-topic variations in Li/Si, B/Si, delta Li-7 and delta B-11 were found in chondrule olivine crystals, but only three chondrules exhibit statistically resolved delta B-11 heterogeneities. Using these three chondrules as a basis for discussion, we evaluated the processes that could potentially cause elemental and isotopic variations of Li and B. We argue that the data can be best understood in the context of condensation of lithium -boron-rich material onto chondrule precursors in (an) initially heterogeneous gaseous reservoir(s), which could be realized if the Solar System derived B-11-rich components from a supernova or supernovae. (c) 2022 Published by Elsevier Ltd.

Automated summary

The origin of the B-11/B-10 ratio in the Solar System is still unknown. While it was previously believed that boron was derived from continuous spallation nucleosynthesis, the B-11/B-10 ratio of the produced boron does not match the solar ratio. Two hypotheses suggest that B-11-rich components may come from low-energy spallation in the Sun's parental molecular cloud or the neutrino process during supernova explosions.